JP2005293777A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it easy to make an optical pickup device compatible with, specially, a medium whose protection substrate is thick when a plurality of information recording media are handled by using a plurality of wavelengths. <P>SOLUTION: A divergence angle varying element which comprises two lenses and moves one lens along an optical axis to vary the angle of divergence of light flux is arranged in an optical path to correct a spherical aberration due to refractive index variation accompanying variance in protection layer thickness, wavelength variance, and temperature variation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup device and an optical element used for the optical pickup device, and more particularly to an optical pickup device suitable for writing information on an optical disc having a plurality of layers.

  From the past to the present, information is reproduced and recorded on optical information recording media (also called optical discs or media) such as CDs (compact discs) and DVDs (digital video discs or digital versatile discs). Optical pickup devices (also referred to as optical heads, optical head devices, etc.) for carrying out have been developed and manufactured, and are in widespread use.

  Recently, research and development have also been conducted on a standard of an optical information recording medium that can record information at a higher density using a light source having a wavelength of about 405 nm.

  In such an optical pickup device, a light beam emitted from a light source (mainly a laser diode is used) is converted into an optical disk via an optical system including optical elements such as a beam shaping prism, a collimator, a beam splitter, and an objective optical element. The light is condensed on the information recording surface to form a spot, and the reflected light from the information recording hole (also referred to as pit) on the recording surface is condensed again on the sensor through the optical system, and converted into an electric signal. Information is reproduced by converting. At this time, since the light flux of the reflected light also changes depending on the shape of the information recording hole, information of “0” and “1” is distinguished using this. Note that a protective substrate (a protective layer made of plastic, also referred to as a cover glass or simply a substrate) is provided on the information recording surface of the optical disc.

  When information is recorded on a recording medium such as a CD-R or CD-RW, a spot due to a laser beam is formed on the recording surface to cause a thermochemical change in the recording material on the recording surface. Thus, for example, in the case of CD-R, the heat diffusible dye is irreversibly changed to form the same shape as the information recording hole. In the case of CD-RW, since a phase change material is used, information can be rewritten because it changes reversibly between a crystalline state and an amorphous state by a thermochemical change.

  In an optical pickup device for reproducing information from a CD standard optical disk, the NA of the objective lens is around 0.45, and the wavelength of the light source used is around 785 nm. For recording, a recording material of about 0.50 is often used. The protective substrate thickness of the CD standard optical disk is 1.2 mm.

  Now, CD is widely used as an optical information recording medium, but DVD has been popular for several years. This is an increase in the amount of information recorded by making the protective substrate thinner than the CD and further reducing the information recording hole. The CD is about 600 to 700 MB (megabytes), but about 4 .7 GB (gigabytes), which has a large recording capacity, and is often used as a distribution medium for recording moving images such as movies.

  An optical pickup device for reproducing information from a DVD standard optical disc is in principle the same as that for a CD, but the NA of the objective lens is reduced because the information recording hole is small as described above. Is around 0.60, and the wavelength of the light source used is around 655 nm. Also, for recording, those with a value of about 0.65 are often used. The protective substrate thickness of the DVD standard optical disk is 0.6 mm.

  Also, recordable optical discs of the DVD standard have already been put into practical use, and there are various standards such as DVD-RAM, DVD-RW / R, and DVD + RW / R. The technical principle regarding these is also the same as in the CD standard.

  Two types of standards have been proposed for large-capacity optical disks using a blue-violet light source having a wavelength of about 405 nm. One is a Blu-Ray Disc (also referred to as BD) in which the disc substrate thickness is 0.1 mm and the NA of the objective lens is about 0.85, and the other is the disc substrate thickness is 0.6 mm. The HD-DVD has an NA of about 0.65. In either case, the capacity is about 20 GB (gigabyte) in a single layer. In these standards, the signal reading / recording is the same as the conventional standards in principle.

  Now, there is a demand for compatibility between a large-capacity optical disk using such a blue-violet laser light source and existing CDs and DVDs, and information is reproduced and / or recorded particularly through the same objective optical element. It is required to be able to

  In this case, correction of spherical aberration based on the substrate thickness difference of each medium and correction of aberration based on the wavelength difference are necessary, and various methods have been proposed in the past, but it is not easy to make the three media compatible. Absent.

  Basically, an objective optical element is designed on the basis of the medium having the largest NA, and correction is performed on other media.

  In Patent Document 1, in order to cope with optical disks having different protective substrate thicknesses, an optimal condensing spot is formed for each optical disk having different protective substrate thicknesses by using a diffraction structure which is a kind of optical path difference providing structure. The technique to do is disclosed (refer patent document 1).

  Further, in Patent Document 2, in order to cope with optical disks having different protective substrate thicknesses, by changing the magnification of the light beam incident on the objective lens by driving a collimator or the like, for each optical disk having different protective substrate thicknesses. A technique for forming an optimum focused spot is disclosed (see Patent Document 2).

JP 2001-60336 A

JP-A-9-17023

  In general, in an optical pickup device, the light beam incident on the objective optical element is most preferably infinite parallel light. Generally, the divergent light beam emitted from the light source is collimated by a collimator lens and then incident on the objective optical element. The structure to make it take is taken. In this case, when an element having a diffractive structure is arranged in the optical path, there is an advantage that loss of light quantity due to vignetting can be prevented.

  However, as in the technique of Patent Document 1, if an attempt is made to eliminate the difference in thickness between the three types of protective substrates using a diffractive structure, different-order diffracted light will be used, resulting in a decrease in diffraction efficiency and an insufficient amount of light. Therefore, a problem occurs in the formation of the condensed spot.

  Furthermore, since the correction amount for the CD having the thickest substrate and the smallest NA becomes large, there is a problem that the WD becomes short when infinite parallel light is incident on the objective optical element (WD = working distance, operation). The distance between the most protruding part of the objective optical element on the disk side and the disk). If the WD is short, there is a high possibility that the disc will collide with the objective optical element, which is not preferable in terms of the pickup structure.

  By the way, in order to reduce costs and save space, a configuration in which finite divergent light is incident on an objective optical element has been adopted. Such “finite” is a single medium (light The problem is relatively small when recording / reproducing only the information recording medium).

  Then, as in Patent Document 2, it is possible to generate a spherical aberration by changing the magnification of the light beam incident on the objective lens, and cancel the spherical aberration based on the substrate thickness difference to form a focused spot. In this case, the WD can be ensured for a long time by making the CD a finite divergent light.

  However, when finite divergent light is incident on the objective lens, coma aberration occurs when the objective lens tracks, because the light beam is obliquely incident (not generated in the case of infinite parallel light). In particular, in the case of a compatible objective optical element that supports recording / reproduction of a plurality of standards, there is a problem that the tracking characteristic deteriorates as the correction amount from the reference objective lens increases.

  In addition, when the optical element is moved back and forth in the optical path, the wavefront changes, and an undesired aberration may occur in some cases. Therefore, the optical surface of the advancing / retreating optical element needs to have a shape that does not cause aberrations, which increases the degree of difficulty in optical design.

  However, the above technique does not suggest or disclose any deterioration in tracking characteristics, improvement thereof, or reduction of aberration caused by an element moving forward and backward in the optical path.

  Therefore, in the present invention, for the three types of media, in an optical system that achieves compatibility with a single optical element, while ensuring WD for the media with the thickest substrate thickness, tracking characteristics do not deteriorate, An object of the present invention is to realize an optical pickup device in which the aberration state does not change.

  As a result of the study, the inventors of the present application have made the divergence angle conversion element, which is an optical element existing in the optical path and emits by changing the divergence angle of the incident light beam, exist in the optical path or retract as necessary. In other words, it has been found that compatibility of a plurality of information recording media can be achieved without changing the aberration and while maintaining a working distance.

  According to such a configuration, it is possible to cope with a plurality of information recording media with only a single objective optical element without requiring a diffractive element having a fine structure, ensuring WD and good tracking characteristics, It is possible to realize an aberration state.

  In order to solve the above-described problems, in the optical pickup device according to the present invention, information is reproduced and / or recorded on the first information recording medium having the protective substrate thickness t1 using the light beam emitted from the first light source having the wavelength λ1. The information is reproduced and / or recorded on the second information recording medium having the protective substrate thickness t2 (t1 ≦ t2) using the light beam emitted from the second light source having the wavelength λ2 (λ1 <λ2). An optical pickup device that reproduces and / or records information on a third information recording medium having a protective substrate thickness t3 (t2 <t3) using a light beam emitted from a third light source having λ3 (λ2 <λ3). In order to condense the light beam emitted from each light source onto the information recording surface of each information recording medium, the objective optical element used in common and the first to third light sources to the objective optical element. Light path Between the first divergence angle changing element that changes the divergence angle of the incident light beam and emits the light, and the optical path from the first to third light sources to the objective optical element. A second divergence angle changing element that is movable between a first position and a second position outside the optical path and is arranged at the first position to change the divergence angle of the incident light beam and emits the same; When information is reproduced and / or recorded on the first information recording medium, a light beam of infinite parallel light is incident on the objective optical element, and information is reproduced and / or recorded on the third information recording medium. When performing, a light beam of finite divergent light is incident on the objective optical element, and the second divergence angle changing element is used depending on whether the magnification of the light beam incident on the objective optical element is infinite parallel light or finite divergent light. The arrangement position is different.

  According to such a configuration, since the second divergence angle conversion element changes the position on the optical path and outside the optical path between the first information recording medium and the third information recording medium, the optical action is changed, and the objective is changed. The divergence angle of the light beam entering the optical element also changes. Therefore, it is possible to correct the spherical aberration due to the difference in substrate thickness only by this. In addition, infinite parallel light or finite divergent light can be incident on the second information recording medium as necessary.

  In a specific aspect of the present invention, when information is reproduced and / or recorded on the first information recording medium and the second information recording medium, the second divergence angle changing element is at the first position. It is characterized by being arranged.

  In another specific aspect of the invention, the second divergence angle changing element has a negative refractive power.

  In another specific aspect of the present invention, when the information is reproduced and / or recorded on the first information recording medium and the second information recording medium, the second divergence angle changing element is the second divergence angle changing element. It is arranged at a position.

  In another specific aspect of the present invention, the second divergence angle changing element has a positive refractive power.

  In another specific aspect of the invention, the second divergence angle changing element is one of elements constituting a beam expander.

  In particular, if the beam expander is composed of a convex lens (positive lens) and a concave lens (negative lens), there is an advantage that the distance in the optical axis direction can be shortened, and either one can be adopted as the second divergence angle changing element. .

  In another specific aspect of the present invention, the second divergence angle changing element is a coupling lens.

  In another specific aspect of the present invention, the coupling lens is a collimating lens.

  With this configuration, the divergence angle of the light beam incident on the objective optical element is increased by retracting the coupling lens having a positive refractive power from the inside and outside of the optical path, so that the third information recording medium can be applied to the third information recording medium. Compatibility can be achieved.

  In another specific aspect of the present invention, among the optical elements present in the optical path, an optical element having a negative refractive power is advanced and retracted to switch the recording layer of an information recording medium having a plurality of recording layers. It is characterized by performing.

  In this way, the divergence angle can be minutely changed by moving the concave lens forward and backward in the optical axis direction, and the recording layer can be switched for the recording medium corresponding to two layers.

  In another specific aspect of the present invention, the first divergence angle changing element performs position switching in the optical axis direction.

  With this configuration, the divergence angle of the light beam incident on the objective optical element can be changed more dynamically, and compatibility with the three information recording media can be easily achieved.

  In another specific aspect of the present invention, as the second divergence angle changing element moves between the first element and the second position, the first divergence angle changing element is positioned in the optical axis direction. It is characterized by switching.

  If comprised in this way, the divergence angle of the light beam which injects into an objective optical element can be variously changed further.

  In another specific aspect of the present invention, information is reproduced and / or recorded on the first information recording medium, and information is reproduced and / or recorded on the second information recording medium. In some cases, the position of the first divergence angle changing element is switched in the optical axis direction.

  In another specific aspect of the present invention, when information is reproduced and / or recorded on the first information recording medium and the second information recording medium, information is recorded on the third information recording medium. The position of the first divergence angle changing element in the direction of the optical axis is switched between reproduction and / or recording.

  In another specific aspect of the present invention, the optical path is arranged between the first to third light sources and the optical path from the objective optical element to the third position on the optical path and movable to the fourth position outside the optical path. And when it arrange | positions in the said 3rd position, it has the 3rd divergence angle change element which changes and radiates | emits the divergence angle of incident light beam, It is characterized by the above-mentioned.

  In this way, the divergence angle of the light beam incident on the objective optical element can be changed in various ways, and is also suitable for correction.

  For example, if the collimator or coupling lens is moved back and forth in the optical axis direction as the first divergence angle changing element, the focus position changes. At this time, the divergent lens is arranged on the optical path to correct it. It can be performed.

  Similarly, a function of correcting aberrations caused by other optical elements such as a collimator and a coupling lens (due to temperature and due to difference in wavelength used) can be provided.

  In another specific aspect of the present invention, the second divergence angle changing element and the third divergence angle changing element are exclusively located on the optical path.

  With this configuration, for example, (1) only the first divergence angle changing element is present in the optical path, and (2) only the second divergence angle changing element is present in the optical path. The system can be switched.

  In another specific aspect of the present invention, the second divergence angle changing element and the third divergence angle changing element are located on the optical path at the same time or separated from the optical path at the same time to constitute an optical system. It is characterized in that there is a case.

  With this configuration, for example, (1) both the first divergence angle changing element and the second divergence angle changing element are arranged in the optical path, and (2) only the first divergence angle changing element is in the optical path. (3) Only the second divergence angle changing element is present in the optical path, and the three types of optical systems can be switched. Of course, in the case of (1), both may be retracted from the optical path, or the four types of optical systems may be switched by adding this.

  In another specific aspect of the invention, the objective optical element is optimized for the first information recording medium.

  In another specific aspect of the present invention, the objective optical element is optimized for both the first information recording medium and the second information recording medium.

  With this configuration, it is only necessary to achieve compatibility by changing the divergence angle only for the third information recording medium, so that the configuration of the entire pickup is simplified.

  In this case, since the wavelength to be used is different, a structure that provides an optical path difference based on the difference in wavelength may be used. Since it is necessary to use a sufficient amount of light and to reduce coma due to tracking, infinite parallel light is incident on both the first information recording medium and the second information recording medium. It is preferable.

  Examples of structures that provide an optical path difference depending on the wavelength difference include a wavelength selective diffraction element, a diffraction element that emits diffracted light of a different order for each wavelength of the light beam, and a phase difference that differs for each wavelength of the light beam. Examples thereof include a phase difference providing structure element (claim 39, claim 40, claim 41).

  A typical optical path difference providing structure is a sawtooth diffractive structure as recited in claim 40.

  This is a concentric fine step with the optical axis as the center, and the light flux that has passed through the adjacent annular zones is given a predetermined optical path difference.

  By setting the sawtooth pitch (diffraction power) and depth (blazed wavelength), for example, for the first information recording medium, the light beam from the first light source in the specific NA is caused by the eighth-order diffracted light. It is formed as a condensing spot. For the second information recording medium, the light beam from the second light source in the same NA is formed as a condensing spot by the fifth-order diffracted light. However, the luminous flux from the outer area (area above a specific NA) contributes to the formation of a condensed spot in the case of DVD, and flare light in the case of CD and does not contribute to the formation of the condensed spot.

  As described above, in particular, by using light having different diffraction orders, the diffraction efficiency in each case can be increased, and the amount of light can be secured.

  Such a diffractive structure is an example of an optical path difference providing structure, but other known “phase difference providing structure” and “wavelength selective diffractive element (also referred to as multi-level structure)” can also be employed.

  Examples of the phase difference imparting structure include an annular phase correction objective lens system, for example, Japanese Patent Application Laid-Open No. 11-2759 and Japanese Patent Application Laid-Open No. 11-16190.

  Japanese Patent Laid-Open No. 11-2759 describes that the surface shape of the basic objective lens is set to be optimum for DVD recording / reproduction as described above, and is based on a phase correction method for CD recording / reproduction. This is a case where correction is performed. In other words, an annular step is formed on the surface of the objective lens designed to minimize the wavefront aberration in the DVD system, and the wavefront aberration in the CD system is reduced while suppressing an increase in wavefront aberration in the DVD system. is there.

  In this technique, since the phase control element hardly changes the phase distribution with respect to the DVD wavelength, the RMS wavefront aberration maintains the value of the objective lens optimally designed for the DVD system, and the RMS wavefront aberration of the CD system is reduced. Therefore, the recording / reproducing performance is effective for a DVD system sensitive to wavefront aberration.

  On the other hand, the optical performance of the basic objective lens is set so as to be optimal in CD recording / reproduction, and correction by the phase correction method is performed for DVD recording / reproduction. In the issue.

  Both of these have improved RMS (Root Mean Square) wavefront aberrations for both DVD recording and playback and CD recording and playback.

  In the case of an annular phase correction objective lens, for example, in Japanese Patent Laid-Open No. 11-16190, an optical disk having a substrate thickness intermediate between CD and DVD is assumed, so that it is optimal for recording and reproduction of such an optical disk. In this case, the surface shape of a simple objective lens is set, and RMS (Root Mean Square) wavefront aberration correction for both DVD and CD is performed by a phase correction method.

  Japanese Patent Laid-Open No. 2001-51192 discloses a technique for reducing the RMS (Root Mean Square) wavefront aberration and changing the focal position of the light beam to one point by changing the step amount and surface shape of each annular zone. Yes.

  Further, the “wavelength selective diffraction element (also referred to as a multi-level structure)” is also referred to as a superposition type diffraction structure because it is a shape in which a stepped shape having a predetermined number of steps is periodically repeated. The number of steps, the height and width (pitch) of the steps can be set as appropriate, and are described, for example, in JP-A-9-54973. With such a staircase structure, it is possible to selectively produce a diffractive action for a plurality of wavelengths. And it does not diffract with respect to other wavelengths, and it becomes transparent and does not produce optical action.

  Here, an optical path difference providing structure is used for the purpose of correcting spherical aberration based on the difference in substrate thickness of the optical disc format, but not only that, but also correction of aberration caused by refractive index change due to operating temperature, wavelength of operating wavelength Of course, it can also be used to correct aberrations that occur due to differences or variations in the wavelength used (mode hop). In particular, in the case of aberration due to a wavelength difference, the former is correction of spherical chromatic aberration that occurs based on a wavelength difference of 50 nanometers or more, and the latter is correction of minute wavelength fluctuations within 5 nm.

  In this example, the example in which the diffractive structure is provided in the objective optical element has been described, but it is of course possible to provide it in other elements such as a collimator and a coupling lens.

  It is most preferable to use such a material for an optical element having a refractive surface and an aspherical surface.

  In another specific aspect of the present invention, the first light source to the third light source are light source units housed in a single package.

  If configured in this manner, since the elements existing in the optical path can be used together, the configuration of the entire pickup is simplified.

  According to the present invention, in an optical pickup device that achieves compatibility with a plurality of information recording media, a diffraction element having a fine structure is not necessarily required, and an optical element is placed in an optical path as necessary. An optical pickup device that can ensure WD, have good tracking characteristics, and realize a good aberration state can be obtained without causing a significant change or deterioration of the aberration even when it is made to exist or retract.

[First Embodiment]
FIG. 1 is a diagram schematically showing a configuration of a first optical pickup device PU1 capable of appropriately recording / reproducing information on any of the high density optical disc HD, DVD, and CD. FIG. 1A shows an optical path diagram when information is recorded / reproduced on the high-density optical disc HD and DVD, and FIG. 1B shows an optical path diagram when information is recorded / reproduced on the CD. The optical specification of the high-density optical disc HD is the wavelength λ1 = 408 nm, the thickness t1 of the protective layer PL1 is 0.0875 mm, and the numerical aperture NA1 = 0.85. The optical specification of the DVD is the wavelength λ2 = 658 nm, protection The layer PL2 has a thickness t2 = 0.6 mm and a numerical aperture NA2 = 0.65. The optical specification of the CD is a wavelength λ3 = 785 nm, the protective layer PL3 has a thickness t2 = 1.2 mm, and a numerical aperture NA3 = 0. .45. However, the combination of the wavelength, the thickness of the protective layer, and the numerical aperture is not limited to this.

  The optical pickup device PU1 emits a 408 nm laser beam (first beam) and emits a 408 nm laser beam (first beam) when recording / reproducing information on the high-density optical disk HD, and a DVD. Information is recorded / reproduced with respect to the second light emitting point EP2 (second light source) that emits a laser beam (second light beam) of 658 nm and is emitted when information is recorded / reproduced. And a first light receiving portion EP3 (third light source) that emits a 785 nm laser light beam (third light beam) and a first light receiving unit that receives the reflected light beam from the information recording surface RL1 of the high-density optical disk HD. DS1, a second light receiving unit DS2 that receives a reflected light beam from the information recording surface RL2 of the DVD, a third light receiving unit DS3 that receives a reflected light beam from the information recording surface RL3 of the CD, and a prism PS. Objective optical system OBJ, which is composed of a laser module LM formed, an aberration correction element L1 having a superposed diffractive structure formed on its optical surface, and a condensing element L2 having both aspheric surfaces. The first actuator AC1, the collimating lens COL, the expander lens EXP including the negative lens E1 and the positive lens E2, and the negative lens E1 are driven in the optical axis direction. A second actuator AC2 for driving, a second actuator AC3 (not shown) for driving the positive lens E2 in the direction perpendicular to the optical axis, and a holding member B for integrating the objective optical system OBJ and the aperture limiting element AP. , And.

Next, the configuration of the objective optical element OBJ will be described. The condensing element L2 is a lens dedicated to the high density optical disc HD in which the spherical aberration correction is optimized with respect to the wavelength λ1 and the thickness t1 of the protective layer. The superposition type diffractive structure formed on the optical surface on the laser module LM side of the aberration correction element L1 corrects spherical aberration due to the difference between the thickness t1 of the protective layer PL1 and the thickness t2 of the protective layer PL2. This is the structure. This superposition type diffractive structure is composed of a plurality of annular zones, and each annular zone is divided into five steps. The step Δ of the staircase structure in each ring zone is set to a height that satisfies Δ = 2 · λ1 / (N _λ1 −1). Here, Nλ1 is the refractive index of the aberration correction element L1 at the wavelength λ1. Since the optical path difference added to the first light flux by this staircase structure is 2λ1, the first light flux is transmitted as it is without being affected by the superposition type diffractive structure. Further, since the optical path difference added to the third light flux by this staircase structure is 1λ3, the third light flux is transmitted as it is without being affected by the superposition type diffractive structure. On the other hand, the optical path difference added to the second light flux by this staircase structure is about 0.2λ2, and an optical path difference of just 1λ2 is added to one of the five divided zones, and the first-order diffracted light is Occur. Thus, spherical aberration due to the difference between t1 and t2 is corrected by selectively diffracting only the second light flux.

  Since the superposition type diffractive structure is formed only within the numerical aperture NA2 of the DVD, the second light flux that passes through the area outside the NA2 becomes a flare component on the information recording surface RL2 of the DVD, and the aperture limit for the DVD is limited. Is automatically performed.

  When recording / reproducing information with respect to the high-density optical disk HD in the optical pickup device PU1, the laser module LM is operated to emit the first light emission point EP1. The divergent light beam emitted from the first light emitting point EP1 is reflected by the prism PS as shown by the solid line in FIG. 1A, and is converted into a parallel light beam through the collimator lens COL, and the expander lens EXP. , The diameter of the light beam is enlarged, the diameter of the light beam is regulated by a stop STO (not shown), the light passes through the aperture limiting element AP, and is formed on the information recording surface RL1 via the first protective layer PL1 by the objective optical system OBJ. It becomes a spot to be formed. The objective optical system OBJ performs focusing and tracking by the first actuator AC1 disposed in the periphery thereof. The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective optical system OBJ, the aperture limiting element AP, and the expander lens EXP to be a converged light beam by the collimator lens COL and reflected twice inside the prism PS. The light is condensed on the light receiving part DS1. Then, information recorded on the high density optical disk HD can be read using the output signal of the light receiving unit DS1.

  At this time, the negative lens E1 is driven in the optical axis direction by the uniaxial actuator AC2, thereby correcting the spherical aberration of the spot formed on the information recording surface RL1 of the high-density optical disc HD. The cause of the spherical aberration corrected by adjusting the position of the negative lens E1 is, for example, wavelength variation due to manufacturing error of the first light source, refractive index change or refractive index distribution of the objective optical system OBJ due to temperature change, two-layer disk, 4 Focus jump between information recording layers of a multilayer disk such as a layer disk, thickness variation or thickness distribution due to manufacturing error of the protective layer PL1, and the like.

  Further, when recording / reproducing information with respect to the DVD in the optical pickup device PU1, the negative lens E1 and the positive lens E2 are arranged such that the second light beam is emitted from the expander lens EXP in the state of a parallel light beam. The negative lens E1 is moved by the second actuator AC2 so that the distance between them is larger than that when information is recorded / reproduced with respect to the high-density optical disk HD. Thereafter, the laser module LM is operated to emit the second light emission point EP2. The divergent light beam emitted from the second light emitting point EP2 is reflected by the prism PS as shown by the dotted line in FIG. 1 (a), is converted into a substantially parallel light beam through the collimator lens COL, and the expander lens. By passing through EXP, the diameter of the light beam is expanded and becomes a parallel light beam, and after passing through the aperture limiting element AP, formed by the objective optical system OBJ on the information recording surface RL2 via the second protective layer PL2. Become a spot. The objective optical system OBJ performs focusing and tracking by the first actuator AC1 disposed in the periphery thereof. The reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective optical system OBJ, the aperture limiting element AP, and the expander lens EXP, is converted into a convergent light beam by the collimator lens COL, and is reflected twice inside the prism PS. The light is condensed on the light receiving part DS2. And the information recorded on DVD can be read using the output signal of light-receiving part DS2.

  When recording / reproducing information with respect to the DVD, as in the case of the high-density optical disc HD, the negative lens E1 is driven in the optical axis direction by the second actuator AC2 so as to be on the information recording surface RL2 of the DVD. It is good also as a structure which correct | amends the spherical aberration of the formed spot.

  Further, when recording / reproducing information with respect to the CD in the optical pickup apparatus PU1, the positive lens E2 is moved out of the optical path by the third actuator AC3. Thereafter, the laser module LM is operated to emit the third light emission point EP3. The divergent light beam emitted from the third light emitting point EP3 is reflected by the prism PS as depicted by the two-dot chain line in FIG. 1, and after being converted into a substantially parallel light beam through the collimator lens COL, it is negative. A spot formed on the information recording surface RL3 via the third protective layer PL3 by the objective optical system OBJ after being converted into a divergent light beam by passing through the lens E1 and being regulated by the aperture limiting element AP. Become. The objective optical system OBJ performs focusing and tracking by the first actuator AC1 disposed in the periphery thereof. The reflected light beam modulated by the information pits on the information recording surface RL3 is transmitted again through the objective optical system OBJ, the aperture limiting element AP, and the negative lens E1, is converted into a convergent light beam by the collimator lens COL, and is reflected twice inside the prism PS. The light is condensed on the light receiving unit DS3. And the information recorded on CD can be read using the output signal of light-receiving part DS3. Here, the paraxial power of the negative lens E2 is determined so that the magnification of the objective optical system OBJ is converted to a magnification that corrects the spherical aberration that makes the difference between the thicknesses t1 and t3.

  In the present embodiment, the positive lens E2 is configured to move in the direction perpendicular to the optical axis. However, by rotating the positive lens E2 within a plane perpendicular to the optical axis about a predetermined fulcrum, the positive lens E2 is moved out of the optical path. It is good also as a structure to which it moves.

  Next, an optical system composed of the expander lens and the objective optical system OBJ of the above-described optical pickup device PU1 will be described.

The aspherical surface in this embodiment has a deformation amount from a plane in contact with the apex of the surface as X (mm), a height perpendicular to the optical axis as h (mm), and a radius of curvature as r (mm). , The following formula 1 is expressed by a mathematical formula in which the aspheric coefficient A _2i in Table 1 is substituted. Where κ is the conic coefficient.

また、本実施例における重畳型回折構造は、透過波面に付加される光路差で表される。かかる光路差は、λを入射光束の波長、λ_Ｂを製造波長、光軸に垂直な方向の高さをｈ（ｍｍ）、B_2jを光路差関数係数、ｎを回折次数とするとき次の数２で定義される光路差関数φ_ｂ（ｍｍ）で表される。

In addition, the superposition type diffractive structure in this embodiment is represented by an optical path difference added to the transmitted wavefront. The optical path difference is as follows when λ is the wavelength of the incident light beam, λ _B is the manufacturing wavelength, the height in the direction perpendicular to the optical axis is h (mm), B _2j is the optical path difference function coefficient, and n is the diffraction order. It is represented by an optical path difference function φ _b (mm) defined by Equation 2.

表１において、ＮＡ１、ｆ１、λ１、ｔ１は、それぞれ、高密度光ディスクＨＤ使用時の対物光学系ＯＢＪの開口数、対物光学系ＯＢＪの焦点距離、対物光学系ＯＢＪの波長、対物光学系ＯＢＪの倍率、保護層の厚さであり、ＮＡ２、ｆ２、λ２、ｔ２は、ＤＶＤ使用時の同様の値であり、ＮＡ３、ｆ３、λ３、ｔ３は、ＣＤ使用時の同様の値である。

In Table 1, NA1, f1, λ1, and t1 are the numerical aperture of the objective optical system OBJ, the focal length of the objective optical system OBJ, the wavelength of the objective optical system OBJ, and the objective optical system OBJ, respectively, when the high-density optical disk HD is used. The magnification and the thickness of the protective layer. NA2, f2, λ2, and t2 are the same values when using the DVD, and NA3, f3, λ3, and t3 are the same values when using the CD.

  Further, r (mm) is a radius of curvature, and d1 (mm), d2 (mm), and d3 (mm) are lens intervals when using a high-density optical disk HD, using a DVD, and using a CD, respectively, Nλ1, Nλ2, Nλ3 is the refractive index of the lens with respect to wavelength λ1, wavelength λ2, and wavelength λ3, respectively, and νd is the Abbe number of the d-line lens.

N1, n2, and n3 are the diffraction orders of the diffracted light of the first light beam, the second light beam, and the third light beam generated in the superposition type diffractive structure, respectively.
[Example 1]
The optical system of the first embodiment includes an expander lens composed of a negative lens and a positive lens, both of which are plastic lenses, and an objective optical system composed of an aberration correction element and a condensing element, both of which are plastic lenses. An optical system configured. The specific numerical data is shown in Table 1.

対物光学系は、収差補正素子の光源側の光学面（表１において第５面）に形成した重畳型回折構造の作用により、高密度光ディスクＨＤとＤＶＤとの保護層の厚さの違いによる球面収差を補正したＨＤ／ＤＶＤ互換レンズである。尚、集光素子は、高密度光ディスクＨＤに対して球面収差補正が最適化されたレンズである。

The objective optical system has a spherical surface due to the difference in the thickness of the protective layer between the high-density optical disk HD and the DVD by the action of the superposition type diffractive structure formed on the optical surface (fifth surface in Table 1) on the light source side of the aberration correction element. This is an HD / DVD compatible lens with corrected aberration. The condensing element is a lens in which spherical aberration correction is optimized for the high-density optical disc HD.

This superposition type diffractive structure is composed of a plurality of annular zones, and each annular zone is divided into five steps. The step Δ of the staircase structure in each ring zone is set to a height that satisfies Δ = 2 · λ1 / (N _λ1 −1). Here, Nλ1 is the refractive index of the aberration correction element L1 at the wavelength λ1. Since the optical path difference added to the first light flux by this staircase structure is 2λ1, the first light flux is transmitted as it is without being affected by the superposition type diffractive structure. Further, since the optical path difference added to the third light flux by this staircase structure is 1λ3, the third light flux is transmitted as it is without being affected by the superposition type diffractive structure. On the other hand, the optical path difference added to the second light flux by this staircase structure is about 0.2λ2, and an optical path difference of just 1λ2 is added to one of the five divided zones, and the first-order diffracted light is Occur. Thus, spherical aberration due to the difference between t1 and t2 is corrected by selectively diffracting only the second light flux.

  Incidentally, the diffraction efficiency of the first light beam generated by the superposition type diffractive structure is 100%, the diffraction efficiency of the first light beam of the second light beam is 87%, and the 0th order light beam (transmission) of the third light beam. The diffraction efficiency of light) is 100%, and high diffraction efficiency is obtained for any light flux.

  When recording / reproducing information with respect to a CD, the magnification of the objective optical system can be increased by removing the positive lens of the expander lens from the optical path and moving the negative lens by 1 mm in the direction approaching the objective optical system. Information is recorded / reproduced with respect to the CD after the magnification is adjusted so that the spherical aberration due to the difference in the thickness of the protective layer between the high-density optical disk HD and the CD is corrected.

Further, when the wavelength of the incident light beam changes, the divergence of the light beam emitted from the expander lens changes due to the influence of chromatic aberration. Therefore, at the time of recording / reproducing with respect to the DVD, the negative lens is set so that the distance between the negative lens and the positive lens is wider than that of the high-density optical disk HD so that the second light beam emitted from the expander lens becomes a parallel light beam. It is moving.
[Second Embodiment]
FIG. 2 is a diagram schematically showing a configuration of the second optical pickup device PU2 capable of appropriately recording / reproducing information on any of the high density optical disc HD, DVD and CD. FIG. 2A shows an optical path diagram when recording / reproducing information on the high-density optical disc HD and DVD, and FIG. 2B shows an optical path diagram when recording / reproducing information on the CD. The optical specification of the high-density optical disc HD is the wavelength λ1 = 408 nm, the thickness t1 of the protective layer PL1 is 0.0875 mm, and the numerical aperture NA1 = 0.85. The optical specification of the DVD is the wavelength λ2 = 658 nm, protection The layer PL2 has a thickness t2 = 0.6 mm and a numerical aperture NA2 = 0.65. The optical specification of the CD is a wavelength λ3 = 785 nm, the protective layer PL3 has a thickness t2 = 1.2 mm, and a numerical aperture NA3 = 0. .45. However, the combination of the wavelength, the thickness of the protective layer, and the numerical aperture is not limited to this.

  The optical pickup device PU2 is a first light emitting point EP1 (first light source) that emits a 408 nm laser light beam (first light beam) when recording / reproducing information on the high density optical disk HD, and a DVD. Information is recorded / reproduced with respect to the second light emitting point EP2 (second light source) that emits a laser beam (second light beam) of 658 nm and is emitted when information is recorded / reproduced. And a first light receiving portion EP3 (third light source) that emits a 785 nm laser light beam (third light beam) and a first light receiving unit that receives the reflected light beam from the information recording surface RL1 of the high-density optical disk HD. DS1, a second light receiving unit DS2 that receives a reflected light beam from the information recording surface RL2 of the DVD, a third light receiving unit DS3 that receives a reflected light beam from the information recording surface RL3 of the CD, and a prism PS. Objective optical system OBJ, which is composed of a laser module LM formed, an aberration correction element L1 having a superposed diffractive structure formed on its optical surface, and a condensing element L2 having both aspheric surfaces. The restricting element AP, the first actuator AC1 for driving the objective optical element OBJ to perform focusing / tracking, the collimating lens COL including the first negative lens E1 and the positive lens E2, and the positive lens E2 are switched. The second negative lens E3 inserted in the optical path, a rotation driving device (not shown) for switching between the positive lens E2 and the second negative lens E3 to be inserted in the optical path, and driving the negative lens E1 in the optical axis direction And a holding member B for integrating the objective optical system OBJ and the aperture limiting element AP.

  Since the configuration and function of the objective optical element OBJ are the same as those of the objective optical system OBJ in the first embodiment described above, detailed description thereof is omitted here.

  When recording / reproducing information with respect to the high-density optical disk HD in the optical pickup device PU2, the laser module LM is operated to emit the first light emission point EP1. The divergent light beam emitted from the first light emitting point EP1 is reflected by the prism PS as shown by the solid line in FIG. 2A, and is converted into a parallel light beam through the collimator lens COL. The beam diameter is regulated by the STO, passes through the aperture limiting element AP, and becomes a spot formed on the information recording surface RL1 via the first protective layer PL1 by the objective optical system OBJ. The objective optical system OBJ performs focusing and tracking by the first actuator AC1 disposed in the periphery thereof. The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective optical system OBJ and the aperture limiting element AP, is converted into a convergent light beam by the collimator lens COL, is reflected twice inside the prism PS, and is reflected by the light receiving unit DS1. Condensate. Then, information recorded on the high density optical disk HD can be read using the output signal of the light receiving unit DS1.

  At this time, the spherical aberration of the spot formed on the information recording surface RL1 of the high density optical disk HD is corrected by driving the first lens E1 in the optical axis direction by the uniaxial actuator AC2. The cause of the spherical aberration to be corrected by adjusting the position of the first lens E1 is, for example, wavelength variation due to manufacturing error of the first light source, refractive index change or refractive index distribution of the objective optical system OBJ due to temperature change, two-layer disc, Focus jump between information recording layers of a multilayer disk such as a four-layer disk, thickness variation or thickness distribution due to manufacturing error of the protective layer PL1, and the like.

  Further, when information is recorded / reproduced with respect to the DVD in the optical pickup device PU2, the first negative lens E1 and the positive lens E2 so that the second light beam is emitted from the collimator lens COL in a parallel light beam state. The first negative lens E1 is moved by the second actuator AC2 so that the distance between the second actuator AC2 and the high-density optical disk HD is larger than that when information is recorded / reproduced. Thereafter, the laser module LM is operated to emit the second light emission point EP2. The divergent light beam emitted from the second light emitting point EP2 is reflected by the prism PS as shown by the dotted line in FIG. 2 (a), is converted into a parallel light beam through the collimator lens COL, and the aperture limiting element. After passing through the AP, it becomes a spot formed on the information recording surface RL2 via the second protective layer PL2 by the objective optical system OBJ. The objective optical system OBJ performs focusing and tracking by the first actuator AC1 disposed in the periphery thereof. The reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective optical system OBJ and the aperture limiting element AP, is converted into a convergent light beam by the collimator lens COL, is reflected twice inside the prism PS, and is reflected by the light receiving unit DS2. Condensate. And the information recorded on DVD can be read using the output signal of light-receiving part DS2.

  When recording / reproducing information with respect to a DVD, as in the case of the high-density optical disc HD, the information recording surface RL2 of the DVD is obtained by driving the first negative lens E2 in the optical axis direction by the second actuator AC2. The spherical aberration of the spot formed on the top may be corrected.

Further, when information is recorded / reproduced with respect to the CD in the optical pickup device PU2, a holding member (not shown) on which the positive lens E2 and the second negative lens E2 are mounted is predetermined by a rotation driving device. Spherical aberration in which the magnification of the objective optical system OBJ is the difference between the thicknesses of t1 and t3 after the second negative lens E2 is inserted into the optical path by rotating in a plane perpendicular to the optical axis about the fulcrum. The first negative lens E1 is moved in the direction of the optical axis by the second actuator AC2 so that the magnification is converted so as to be corrected. Thereafter, the laser module LM is operated to emit the third light emission point EP3. The divergent light beam emitted from the third light emitting point EP3 is reflected by the prism PS as shown by the two-dot chain line in FIG. 2, and then passes through the first negative lens E1 and the second negative lens E2. By being transmitted, it is converted into a divergent light beam, and after the light beam diameter is regulated by the aperture limiting element AP, it becomes a spot formed on the information recording surface RL3 via the third protective layer PL3 by the objective optical system OBJ. The objective optical system OBJ performs focusing and tracking by the first actuator AC1 disposed in the periphery thereof. The reflected light beam modulated by the information pits on the information recording surface RL3 is again transmitted through the objective optical system OBJ, the aperture limiting element AP, the second negative lens E2, and the first negative lens E1, and then reflected twice within the prism PS. The light is condensed on the light receiving unit DS3. And the information recorded on CD can be read using the output signal of light-receiving part DS3.
[Third Embodiment]
3 (a) and 3 (b) show information appropriately in a simple configuration for any of the high-density optical disc HD (first optical disc), DVD (second optical disc), and CD (third optical disc). It is a figure which shows schematically the structure of 1st optical pick-up apparatus PU1 which can perform recording / reproduction | regeneration. The optical specifications of the high-density optical disc HD are the first wavelength λ1 = 408 nm, the thickness t1 of the first protective layer PL1 is 0.1 mm, and the numerical aperture NA1 = 0.85. The optical specification of the DVD is the second The wavelength λ2 = 658 nm, the thickness t2 of the second protective layer PL2 = 0.6 mm, the numerical aperture NA2 = 0.60, and the optical specifications of the CD are the third wavelength λ3 = 785 nm and the thickness of the third protective layer PL3. The length t3 = 1.2 mm and the numerical aperture NA3 = 0.45.

  The recording densities (ρ1 to ρ3) of the first optical disc to the third optical disc are ρ3 <ρ2 <ρ1, and the objective when recording and / or reproducing information on the first optical disc to the third optical disc is set. The magnifications (first magnification M1 to third magnification M3) of the optical system OBJ are M1 = M2 = 0 and M3 ≠ 0. However, the combination of wavelength, protective layer thickness, numerical aperture, recording density, and magnification is not limited to this.

  The optical pickup device PU1 of the present embodiment is a first light emitting point LD1 (first light source) that emits a 408 nm laser light beam (first light beam) when recording / reproducing information with respect to the high-density optical disk HD. ), A second light emitting point LD2 (second light source) that emits a 658 nm laser beam (second beam) when recording / reproducing information on a DVD, and a 785 nm laser beam (third). A three-laser one-package 3L1P in which light sources of three different wavelengths composed of a light-emitting point LD3 (third light source) that emits a luminous flux) are integrated in the same package, a photodetector PD, and an optical surface thereof Aberration correction element L1 in which a diffractive structure as a phase structure is formed, and a condensing element in which both surfaces having an aspherical surface have a function of condensing a laser beam transmitted through the aberration correction element L1 on an information recording surface The objective optical system OBJ composed of the child L2, the biaxial actuator AC1, the monoaxial actuator AC2, the stop STO corresponding to the numerical aperture NA1 of the high-density optical disc HD, the polarizing beam splitter PBS, the collimating lens COL (movable element), and the sensor Lens SL, 1/4 wavelength plate QWP, and relay lens RL that can be inserted into and removed from the optical path between the objective optical system OBJ and the collimating lens COL.

  Although not shown, for example, the numerical aperture NA2 of the DVD, which is disposed between the objective optical system OBJ and the stop STO and can be driven integrally or relatively with the objective optical system OBJ by an actuator AC2 or a separate actuator, An aperture limiting element AP for accommodating the numerical aperture NA3 of the CD, and is disposed between the objective optical system OBJ and the collimating lens COL. For example, objective optics associated with wavelength variations due to manufacturing errors of the blue-violet semiconductor laser LD1 and temperature changes. This occurs due to a change in the refractive index of the system OBJ, a refractive index distribution, a focus jump between layers at the time of recording / reproducing on a multi-layer disk such as a two-layer disk, a four-layer disk, a thickness variation due to a manufacturing error of the protective layer PL1, a thickness distribution, etc. Aberration correction means EXP (behind the function of correcting spherical aberration by adjusting its position, etc.) And a beam shaping element SH arranged between the 3 laser 1 package 3L1P and the collimating lens COL, for converting the elliptical light beam from the light source into a circular or substantially circular light beam, to achieve higher performance. An optical pickup device is desirable.

  Further, as shown in FIG. 3C, in the 3 laser 1 package 3L1P, the LD 1 of the first light source that requires the strictest accuracy in the design of the optical system is arranged on the optical axis of the optical pickup device PU1. However, the second light source LD2 and the third light source LD3 may be arranged on the optical axis, or all the light sources may be arranged in balance at a desired position off the axis. Furthermore, in this embodiment, the photodetector PD is provided separately from the 3 laser 1 package 3L1P, but this can also be provided inside the 3 laser 1 package 3L1P or in the vicinity of the 3 laser 1 package 3L1P, thereby Since it is possible to omit the polarization beam splitter PBS, further simplification and cost reduction of the apparatus can be achieved, which is desirable.

  In the optical pickup device PU1, when information is recorded / reproduced with respect to the high-density optical disk HD, the 3 laser 1 package 3L1P is operated to emit the light emission point EP1 of the first light source LD1. Here, after operating the 3 laser 1 package 3L1P to emit the light emission point EP1 of the first light source LD1, the optimum position may be searched while moving the collimating lens COL. The divergent light beam emitted from the first light emitting point EP1 passes through the polarization beam splitter PBS and is converted into a parallel light beam through the collimator lens COL as shown by the solid line in FIG. 3A. The linearly polarized light beam from the light source is converted into a circularly polarized light beam through the quarter-wave plate QWP, the diameter of the light beam is regulated by the stop STO, and the information recording surface RS1 through the first protective layer PL1 by the objective optical system OBJ. It becomes a spot formed on the top. The objective optical system OBJ performs focusing and tracking by a biaxial actuator AC1 disposed around the objective optical system OBJ. The reflected light beam modulated by the information pits on the information recording surface RS1 is transmitted again through the objective optical system OBJ, and the circularly polarized light beam is linearly rotated by 90 ° with the linearly polarized light from the light source via the quarter-wave plate QWP. The light beam is converted into a light beam, is converted into a converged light beam by the collimating lens COL, and is incident on the polarization beam splitter PBS. Here, the polarization beam splitter PBS has, for example, two right-angle prisms bonded together, and the bonded surface is inclined by 45 ° with respect to the optical axis of the optical pickup device PU1, and the bonded surface has S-polarized light. A coating that transmits either one of the P-polarized light (the same direction as the polarization direction of the linearly polarized light beam from 3L1P) and reflects the other polarized light (the direction perpendicular to the polarization direction of the linearly polarized light beam from 3L1P) Has been made. As a result, the light beam that has become a converged light beam by the collimating lens COL is reflected inside the polarization beam splitter PBS and condensed on the photodetector PD via the sensor lens SL. Then, information recorded on the high density optical disk HD can be read using the output signal of the photodetector PD.

  Further, when recording / reproducing information with respect to the DVD in the optical pickup device PU1, the objective optical system OBJ and the collimating lens COL are arranged so that the second light beam is emitted from the collimating lens COL in the state of a parallel light beam. The collimating lens COL is moved by the uniaxial actuator AC2 so that the distance between the two is smaller than that when information is recorded / reproduced with respect to the high-density optical disk HD. Thereafter, the objective optical system OBJ and the 3 laser 1 package 3L1P are operated to emit the light emission point EP2 of the second light source LD2. In this case, the collimator lens COL may be moved while the optimum position is searched after the three lasers 1 package 3L1P is operated to emit the light emission point EP2 of the second light source LD2. Although not shown in FIG. 3A, the divergent light beam emitted from the second light emitting point EP2 is transmitted through the polarization beam splitter PBS, converted into a parallel light beam through the collimator lens COL, and then ¼. A linearly polarized light beam from the light source is converted into a circularly polarized light beam through the wave plate QWP, and becomes a spot formed on the information recording surface RS2 through the second protective layer PL2 by the objective optical system OBJ. The objective optical system OBJ performs focusing and tracking by a biaxial actuator AC1 disposed around the objective optical system OBJ. The reflected light beam modulated by the information pits on the information recording surface RS2 is transmitted again through the objective optical system OBJ, and the circularly polarized light beam is linearly rotated by 90 ° with the linearly polarized light from the light source via the quarter-wave plate QWP. The light beam is converted into a light beam, converted into a converged light beam by the collimator lens COL, reflected inside the polarization beam splitter PBS, and condensed on the photodetector PD through the sensor lens SL. And the information recorded on DVD can be read using the output signal of photodetector PD.

  When recording / reproducing information with respect to the CD, as shown in FIG. 3B, a relay lens RL is inserted between the objective optical system OBJ and the collimating lens COL in the optical path of PU1. The relay lens RL is composed of at least one lens having a positive refractive power, and may be composed of an aspheric lens. Further, the pickup device PU1 includes at least lens driving means (not shown) AC3 for allowing the relay lens RL to be inserted into and removed from the optical path. Such a lens driving means AC3 may be, for example, an axis driving actuator or driving using a cam or helicoid.

  Further, the position when the relay lens RL is inserted is desirably used in the state where the optical axis of the objective optical system OBJ and the optical axis of the relay lens RL are aligned in the optical path of the objective optical system OBJ. The position where the relay lens RL is retracted is preferably used at a lens position where the relay lens RL does not block the light beam incident on the objective optical system OBJ. About these two positions, when the relay lens RL is inserted and when the relay lens RL is retracted, the relay lens RL may be stopped and used at the respective positions, or when the relay lens RL is inserted, In order to correct the tracking shift of the objective optical system OBJ, the relay lens RL may move vertically with respect to the optical axis of the objective optical system OBJ or may move to a state inclined with respect to the optical axis.

  In FIG. 3B, when information is recorded / reproduced with respect to the CD in the optical pickup apparatus PU1, the objective optical system OBJ is set so that the third light beam is emitted from the collimator lens COL in the state of a parallel light beam. The collimating lens COL is moved by the uniaxial actuator AC2 so that the distance between the collimating lens COL and the collimating lens COL is smaller than that when information is recorded / reproduced with respect to the high-density optical disc HD or DVD. Thereafter, a relay lens is inserted to operate the objective optical system OBJ and the 3 laser 1 package 3L1P to emit the light emission point EP3 of the third light source LD3. In this case, the collimator lens COL may be moved while the optimum position is searched after the three lasers 1 package 3L1P is operated to emit the light emission point EP3 of the third light source LD3. The divergent light beam emitted from the third light emitting point EP3 passes through the polarization beam splitter PBS and is converted into a parallel light beam through the collimator lens COL, as shown by the solid line in FIG. 3B. , And enters the inserted relay lens RL. Here, the relay lens RL is configured so that the collimated light beam has a desired image formation magnification M3 (M3 ≠ 0) when the objective optical system OBJ is used for the CD (mainly spherical aberration is corrected). The object point position of the system OBJ is converted, and the light beam is once imaged to work so that the divergent light beam enters the objective optical system OBJ. Further, here, the quarter wavelength plate QWP is disposed between the relay lens RL and the objective optical system OBJ, and converts the linearly polarized light beam from the light source into a circularly polarized light beam, which is the same between the collimating lens COL and the relay lens RL. You may arrange | position between.

  The light beam transmitted through the relay lens is incident on the objective optical system OBJ as a divergent light beam and becomes a spot formed on the information recording surface RS3 by the objective optical system OBJ via the third protective layer PL3. The objective optical system OBJ performs focusing and tracking by a biaxial actuator AC1 disposed around the objective optical system OBJ. The reflected light beam modulated by the information pits on the information recording surface RS3 is transmitted through the objective optical system OBJ again, and then the circularly polarized light beam is rotated 90 ° with the linearly polarized light from the light source via the quarter-wave plate QWP. It is converted into a linear light beam, converted into a parallel light beam by the relay lens RL, converted into a convergent light beam by the collimator lens COL, reflected inside the polarization beam splitter PBS, and condensed on the photodetector PD through the sensor lens SL. And the information recorded on CD can be read using the output signal of photodetector PD.

  Next, the configuration of the objective optical system OBJ will be described.

  The objective optical system OBJ has a phase structure on any one of the optical surfaces in the optical system in order to cope with a plurality of types of optical disks with one optical system.

  The phase structure described above may be either a diffractive structure or an optical path difference providing structure. As schematically shown in FIG. 4, the diffractive structure includes a plurality of annular zones 100 and has a sawtooth shape in cross section including the optical axis, or a step 101 as schematically shown in FIG. 5. Are formed of a plurality of annular zones 102 having the same effective diameter, and the cross-sectional shape including the optical axis is a staircase shape, or a staircase structure is formed inside as schematically shown in FIG. 7 or a plurality of annular zones 105 in which the direction of the step 104 is changed in the middle of the effective diameter as shown schematically in FIG. 7, and the cross-sectional shape including the optical axis is a staircase. Some are in shape. Further, as schematically shown in FIG. 7, the optical path difference providing structure is composed of a plurality of annular zones 105 in which the direction of the step 104 is changed in the middle of the effective diameter, and the cross-sectional shape including the optical axis is a staircase shape. There is. Therefore, the structure schematically shown in FIG. 7 may be a diffractive structure or an optical path difference providing structure. 4 to 7 schematically show the case where each phase structure is formed on a plane, but each phase structure may be formed on a spherical surface or an aspherical surface.

  In the present embodiment, the objective optical system OBJ is composed of a two-group lens including an aberration correction element L1 and a condenser lens L2.

  The aberration correction element L1 is a plastic lens having a refractive index nd of d09 of 1.5091, an Abbe number νd of 56.5, a refractive index with respect to λ1 of 1.5242, and a refractive index with respect to λ2 of 1.5064. , Λ3 has a refractive index of 1.5050. The condensing element L2 is a plastic lens having a refractive index nd of 1.5435 at the d-line and an Abbe number νd of 56.3. In addition, there are flange portions FL1 and FL2 formed integrally with the optical function portion around each optical function portion (the region of the aberration correction element L1 and the condensing element L2 through which the first light beam passes) The flange portions FL1 and FL2 are integrated by joining a part thereof.

  In addition, when integrating the aberration correction element L1 and the condensing element L2, you may integrate both through the lens frame of another member.

  As shown in FIG. 8, the optical surface S1 of the aberration correction element L1 on the semiconductor laser light source side includes a first area AREA1 including an optical axis corresponding to the area in NA2, and a second area corresponding to the area from NA2 to NA1. The first area AREA1 is divided into a plurality of zones with a step structure formed therein, as shown in FIGS. 6A and 6B, with the optical axis as the center. A diffractive structure HOE that is an arrayed structure (hereinafter, this diffractive structure is referred to as “diffractive structure HOE”) is formed.

In the diffraction structure HOE formed in the first area AREA1, the depth D of the staircase structure formed in each annular zone is
D · (N1-1) / λ1 = 2 · q (3)
The number of divisions P in each annular zone is set to 5. However, λ1 represents the wavelength of the laser beam emitted from the first light emitting point EP1 in units of micron (here, λ1 = 0.408 μm), and N1 represents the medium refraction of the aberration correction element L1 with respect to the wavelength λ1. The rate q is a natural number.

  When the first light flux having the first wavelength λ1 is incident on the step structure in which the depth D in the optical axis direction is set in this way, an optical path difference of 2 × λ1 (μm) is generated between the adjacent step structures. The first light beam is transmitted without being diffracted because no substantial phase difference is given (referred to as “0th-order diffracted light” in this specification).

  In addition, when a third light flux having a third wavelength λ3 (here, λ3 = 0.785 μm) is incident on the staircase structure, (2 × λ1 / (N1-1) · ( An optical path difference of (N3-1) / λ3) × λ3 (μm) occurs. N3 is a medium refractive index of the aberration correction element L1 with respect to the wavelength λ3. Since (N3-1) / λ3 is approximately twice (N1-1) / λ1 in the third wavelength λ3, an optical path difference of approximately 1 × λ3 (μm) occurs between adjacent staircase structures. Similarly to the first light beam, the light beam is not diffracted and is transmitted as zero-order diffracted light because no phase difference is substantially given.

  On the other hand, when a second light flux having a second wavelength λ2 (here, λ2 = 0.658 μm) is incident on the staircase structure, {2 × λ1 / (N1-1) × ( N2-1) / λ2} × λ2 = {2 × 0.408 / (1.52422-1) × (1.5064-1) /0.658} × λ2 = 1.199 · λ2 (μm) A difference occurs. Since the number of divisions P in each annular zone is set to 5, an optical path difference corresponding to one wavelength of the second wavelength λ2 occurs between adjacent annular zones ((1.199-1) × 5≈ 1) The second light beam is diffracted in the + 1st order direction (+ 1st order diffracted light). At this time, the diffraction efficiency of the + 1st order diffracted light of the second light flux is 87.5%, but the amount of light is sufficient for recording / reproducing information with respect to the DVD.

  The condensing element L2 is designed so that the spherical aberration is minimized with respect to the combination of the first wavelength λ1, the magnification M1 = 0, and the first protective layer PL1. Therefore, when the first magnification M1 for the first light flux and the second magnification M2 for the second light flux are set to the same 0 as in the present embodiment, the thicknesses of the first protective layer PL1 and the second protective layer PL2 Due to the difference, the spherical aberration of the second light flux that has passed through the condensing element L2 and the second protective layer PL2 becomes in the overcorrected direction.

  The width of each annular zone of the diffractive structure HOE provided on the optical surface S1 on the semiconductor laser light source side of the aberration correction element L1 is a spherical surface in the direction of insufficient correction with respect to the + 1st order diffracted light by the diffractive action when the second light beam is incident. The aberration is set to be added. The added amount of spherical aberration due to the diffractive structure HOE and the spherical aberration in the overcorrection direction caused by the difference in thickness between the first protective layer PL1 and the second protective layer PL2 cancel each other, so that the diffractive structure HOE and the second protection are The second light beam transmitted through the layer PL2 forms a good spot on the information recording surface RS2 of the DVD.

  In this embodiment, the optical surface S1 on the semiconductor laser light source side of the aberration correction element L1 is a diffractive structure HOE. However, at least one phase structure is provided on the optical surface S2 on the optical disk side of the aberration correction element L1 and the light condensing element L2. The second area AREA2 of the semiconductor laser light source side optical surface S1 of the aberration correction element L1 and / or the third area AREA3 and / or the fourth area AREA4 of the optical surface S2 of the optical disc, and / or the condenser lens. L2 includes a diffractive structure (hereinafter referred to as “diffractive structure DOE”) composed of a plurality of annular zones having a sawtooth cross-section including the optical axis as shown in FIGS. 4 (a) and 4 (b). )) May be formed.

  The diffractive structure DOE is a structure for suppressing the chromatic aberration of the objective optical system OBJ in the blue-violet region and the change in spherical aberration due to the temperature change, which are particularly problematic when the condensing element L2 is formed of a plastic lens. .

  In the diffractive structure DOE, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of the desired order diffracted light is 100% with respect to the wavelength of 390 nm to 420 nm. When the first light beam is incident on the diffractive structure DOE in which the step depth is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected. For example, the diffraction efficiency of the diffracted light of the desired order is designed to be 100% with respect to the wavelength of 390 nm (the refractive index of the aberration correction element L1 with respect to the wavelength of 390 nm is 1.5273). When the first light beam enters the diffractive structure DOE in which the depth of the step is set in this way, + 2nd order diffracted light is generated with a diffraction efficiency of 96.8%, and when the second light beam enters, the + 1st order diffracted light is generated. Occurs at a diffraction efficiency of 93.9%, so that sufficient diffraction efficiency is obtained in any wavelength region, and even when chromatic aberration is corrected in the blue-violet region, chromatic aberration correction in the wavelength region of the second light flux is excessive. Not too much. Here, the diffraction efficiency is distributed to the first light flux and the second light flux. However, by optimizing the first wavelength λ1, the diffraction efficiency of the first light flux may be emphasized.

  In the objective optical system OBJ in the present embodiment, such a diffractive structure DOE is not provided. These diffractive structures DOE may be provided on the optical surface of the light condensing element L2 in addition to the second areas AREA2 and S2. In this case, the diffractive structure DOE may be a single diffractive structure DOE with the entire optical surface S2 on the optical disc side of the aberration correction element L1 as one region. The optical surface S2 on the optical disc side of the aberration correction element L1 is shown in FIG. As shown in FIG. 8C, two different concentric regions (AREA3 and AREA4) centering on the optical axis, or in some cases, three regions may be provided with different diffractive structures DOE in the respective regions. Further, the entire optical surface in which the diffractive structure DOE is provided by the light condensing element L2 may be used as one region, so that one diffractive structure DOE may be formed. As the two or three concentric regions, different diffractive structures DOE may be provided in each region. The diffraction efficiencies in the respective regions at this time may be set such that the diffraction efficiencies are distributed to the first light flux and the third light flux in the region where the first light flux and the third light flux are transmitted in common (for example, the height of the step). Is designed so that the diffraction efficiency is 100% with respect to the wavelength of 390 nm (the refractive index of the aberration correction element L1 with respect to the wavelength of 390 nm is 1.5273). When the second light beam is incident with a diffraction efficiency of 96.8%, the + 1st order diffracted light is generated with a diffraction efficiency of 93.9%. When the third light beam is incident, the + 1st order diffracted light is 99.2% diffracted. If the diffraction efficiency is distributed between the first light flux and the second light flux in a region where the first light flux and the second light flux are transmitted in common, it is possible to distribute the diffraction efficiency. good. Further, by optimizing with respect to the first wavelength λ1, a configuration in which the diffraction efficiency of the first light flux is emphasized may be adopted.

  Further, in the diffractive structure DOE, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration becomes the overcorrection direction. It has the wavelength dependence of spherical aberration that changes to Thereby, the usable temperature range of the objective optical system OBJ, which is a high NA plastic lens, is expanded by canceling out the spherical aberration change generated in the light condensing element with the environmental temperature change.

  The objective optical system of the present embodiment has a two-group configuration of the aberration correction element L1 in which the diffractive structure HOE is disposed on the optical surface S1 on the semiconductor laser light source side and the aspherical condensing lens L2. It may be constituted by a single lens having a structure, and if the objective optical system can be constituted by one piece, it is advantageous for simplification and cost reduction of the apparatus.

  The collimating lens COL is arranged in the common optical path of the first light flux and the third light flux, and is configured such that its position can be shifted in the optical axis direction by the single-axis actuator AC2. As described above, the chromatic aberration between the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 is absorbed, and a light beam of any wavelength can be emitted from the collimator lens COL in the state of a parallel light beam. Furthermore, the spherical aberration of the spot formed on the information recording surface RS1 of the high-density optical disk HD can be corrected by moving the collimating lens COL in the optical axis direction when recording / reproducing information on the high-density optical disk HD. Therefore, it is possible to always maintain good recording / reproducing characteristics for the high-density optical disc HD.

  The cause of the spherical aberration corrected by adjusting the position of the collimating lens COL is, for example, wavelength variation due to manufacturing error of the blue-violet semiconductor laser LD1, refractive index change or refractive index distribution of the objective optical system OBJ due to temperature change, two-layer disk These include focus jumps between layers at the time of recording / reproducing with respect to a multi-layer disc such as a four-layer disc, thickness variation and thickness distribution due to manufacturing errors of the protective layer PL1, and the like.

In the above description, the case where the spherical aberration of the spot formed on the information recording surface RL1 of the high-density optical disk HD is corrected has been described. However, the spherical aberration of the spot formed on the information recording surface RS2 of the DVD is corrected by the collimating lens. You may make it correct | amend by position adjustment of COL.
Numerical examples of the relay lens RL used in the present embodiment are shown in the following [Table 4] to [Table 6].

  [Table 4] to [Table 6] are numerical examples in a case where one embodiment of the relay lens is combined with the objective optical system used in the present embodiment in a state of using the CD.

  As shown in [Table 4] to [Table 6], the relay lens RL used in the present embodiment may be an aspherical plastic single lens. In addition, the relay lens RL may be composed of a plurality of lenses or an objective optical system. When the chromatic aberration of OBJ is large and causes a problem, a phase structure such as a diffraction structure may be provided. However, in view of simplification and cost reduction of the apparatus, it is preferable to configure the lens with an aspherical single lens because it can have a desirable configuration including driving means.

また、本実施の形態では、ＮＡ３に対応した開口制限行うための開口素子として、接合部材Ｂを介して対物光学系ＯＢＪと一体化された開口制限素子ＡＰを備えても良い。そして、２軸アクチュエータＡＣ１により、開口制限素子ＡＰと対物光学系ＯＢＪとを一体にトラッキング駆動させるようにすれば、トラッキング時の性能を良好に維持することが可能となり望ましい。

In the present embodiment, an aperture limiting element AP integrated with the objective optical system OBJ via the bonding member B may be provided as an aperture element for performing aperture limitation corresponding to NA3. If the aperture limiting element AP and the objective optical system OBJ are integrally driven by the biaxial actuator AC1, it is desirable that the performance during tracking can be maintained well.

  On the optical surface of the aperture limiting element AP, a wavelength selection filter WF having wavelength selectivity of transmittance is formed. This wavelength selection filter WF transmits all wavelengths from the first wavelength λ1 to the third wavelength λ3 in the region within NA3, blocks only the third wavelength λ3 in the region from NA3 to NA1, and blocks the first wavelength λ1 and the first wavelength λ1. Since it has wavelength selectivity of transmittance that transmits two wavelengths λ2, aperture restriction corresponding to NA3 can be performed by such wavelength selectivity. Further, when aperture restriction is performed for NA2, at least the first wavelength λ1 and the second wavelength λ2 are transmitted in the region within NA2, and at least the second wavelength λ2 is blocked in the region from NA2 to NA1, and the first wavelength A wavelength selection filter having wavelength selectivity of transmittance that transmits λ1 may be used. Further, in order to provide the NA2 and NA3 aperture limiting function with a single wavelength selection filter, for example, the filter is divided into three concentric regions centered on the optical axis, and the first wavelength is divided in the region within NA3. Transmits all wavelengths from λ1 to third wavelength λ3, blocks only the third wavelength λ3 in the region from NA3 to NA2, and has a wavelength selectivity of transmittance that transmits the first wavelength λ1 and the second wavelength λ2. In the region from NA2 to NA1, the second wavelength λ2 and the third wavelength λ3 may be blocked, and the wavelength selective filter having the wavelength selectivity of the transmittance that transmits the first wavelength λ1 may be used.

  The wavelength selection filter WF may be formed on the optical function surface of the aberration correction element L1, or may be formed on the optical function surface of the light condensing element L2.

  Further, since the diffractive structure HOE is formed in the first area AREA1 corresponding to NA2, the second light flux that passes through the second area AREA2 is a flare that does not contribute to spot formation on the information recording surface RL2 of the DVD. Become an ingredient. This means that the objective optical system OBJ has an aperture limiting function for NA2, and transmission is performed, and aperture limiting corresponding to NA2 is performed by this function.

  Further, as a method of limiting the aperture, not only a method using the wavelength selection filter WF, but also a method of mechanically switching the diaphragm or a method using a liquid crystal phase control element LCD described later.

  Further, it is disposed between the objective optical system OBJ and the collimating lens COL, for example, wavelength variation due to manufacturing error of the blue-violet semiconductor laser LD1, change in refractive index or refractive index distribution of the objective optical system OBJ due to temperature change, two layers Functions such as performing focus correction between layers during recording / reproducing on a multi-layer disk such as a disk, four-layer disk, etc., and correcting spherical aberration caused by thickness variation and thickness distribution due to manufacturing error of the protective layer PL1 by adjusting its position, etc. Aberration correction means EXP (beam expander) having the above may be used.

  The aberration correction means EXP is a beam expander composed of two lens groups, for example, a negative lens group having at least one negative lens and a positive lens group having at least one positive lens. By making at least one of the two lens groups movable in a direction parallel to the optical axis, for example, it is possible to correct spherical aberration caused by the above-described factors. In addition, when the aberration correction means EXP is used, the collimating lens COL can be used without moving. In this case, the collimating lens is used for the difference in the light source wavelength corresponding to each of the high density optical discs HD, DVD, CD. The aberration correction means EXP may be moved so as to correct the chromatic aberration of the lens COL.

  The aberration correction means EXP may be provided with means for correcting chromatic aberration of the objective optical system OBJ. As such means, for example, any optical surface of the aberration correction means EXP may be used to correct chromatic aberration. A phase structure is provided, the dispersion relationship of the lenses constituting the aberration correction means EXP is optimized, or at least one negative lens and at least one positive lens are bonded to one of the lens groups. There is a configuration in which a cemented lens having a configuration is used.

  A beam shaping element SH can also be used. The beam shaping element SH is an element for converting an elliptical light beam from the semiconductor laser into a circular or substantially circular light beam, and the beam shaping element SH is used. Thus, the light utilization efficiency of the light from the semiconductor laser can be improved, and the high performance of the pickup is achieved.

  Such a beam shaping element SH is composed of, for example, a cylindrical single lens having a curvature in only one direction, or an anamorphic surface having different curvature radii in two orthogonal directions.

  When the beam shaping element SH is arranged in the optical path of the three-wavelength integrated laser as in the configuration used in this embodiment, the positional relationship between the three laser emission points and the beam shaping element SH is, for example, a cylindrical surface. It is desirable that the direction of the surface of the beam shaping element having no curvature coincides with the direction in which the three laser emission points are aligned. For example, for a beam shaping element constituted by an anamorphic surface, It is desirable that the direction in which the surface of the beam shaping element has a large curvature coincides with the direction in which the three laser emission points are arranged. By making the positional relationship between the beam shaping element SH and the three laser emission points as described above, it becomes possible to eliminate or reduce the influence of aberration caused by the beam shaping element.

However, depending on the relationship between the arrangement of the laser emission points and the direction of the major axis direction of the elliptical light beam of the semiconductor laser, this is not limited to the above, and the direction of beam shaping by the beam shaping element SH and the direction of the semiconductor laser elliptical light beam are set as desired. Must support multiple light sources.
[Fourth Embodiment]
Here, only the CD as the third information recording medium is compatible by diverging the incident light beam to the objective optical element.

  The objective optical element used here is provided with a DOE that emits different diffracted light based on the wavelength difference for the BD as the first information recording medium and the DVD as the second information recording medium.

  As described above, there is a way to correct spherical aberration with CD (λ = 785 nm, NA0.48, T = 1.2 mm) with an objective lens corrected for aberration with BD (λ = 408 nm, NA0.85, T = 0.0875 mm). It is necessary to make divergent light having a finite magnification M incident on the objective lens. Further, when the BD satisfies the sine condition, there is a problem that the tracking characteristic on the CD side is poor.

  Therefore, by using an optical element that generates a wavefront (over) for correcting spherical aberration on the CD side under the following condition (1) with a finite magnification m on the CD side, coma aberration generated during tracking can be reduced. .

As a method of generating a wavefront for correcting spherical aberration, an optical element is inserted into the optical path only when a CD is used.
Condition (1) 1.2M <m <M
However, M <0
Thereby, it can suppress that it degrades rather than the case without correction | amendment because m is larger than a minimum, and it can improve more than the case without correction | amendment by being smaller than an upper limit.

  Table 7 below shows data of lenses inserted into the optical path.

It is a schematic diagram of the optical pick-up concerning 1st Embodiment. It is a schematic diagram of the optical pick-up in connection with 2nd Embodiment. It is a schematic diagram of the optical pick-up in connection with 3rd Embodiment. It is a schematic diagram of the diffraction element concerning 3rd Embodiment. It is a schematic diagram of the diffraction element concerning 3rd Embodiment. It is a schematic diagram of the diffraction element concerning 3rd Embodiment. It is a schematic diagram of the diffraction element concerning 3rd Embodiment. It is a schematic diagram of an aberration correction element according to the third embodiment.

Explanation of symbols

PU ... Pick-up device, LM ... Light source module, COL ... Collimator (collimating lens), E1 ... Expander lens (negative), E2 ... Expander lens (positive), AC1 ... Actuator, AC2 ... Actuator, B ... Holding member, OBJ ... Objective Optical element, AP ... Aperture limiting element, 3LP1P ... 3 laser 1 package, PBS ... Polarizing beam splitter, RL ... Relay lens, SL ... Sensor lens, QWP ... 1/4 wavelength plate, STO ... Aperture, L1 ... Aberration correction element , L2 ... Light collecting element

Claims (19)

Information is reproduced and / or recorded on the first information recording medium having the protective substrate thickness t1 using the light beam emitted from the first light source having the wavelength λ1.
Information is reproduced and / or recorded on a second information recording medium having a protective substrate thickness t2 (t1 ≦ t2) using a light beam emitted from a second light source having a wavelength λ2 (λ1 <λ2).
An optical pickup device that reproduces and / or records information on a third information recording medium having a protective substrate thickness t3 (t2 <t3) using a light beam emitted from a third light source having a wavelength λ3 (λ2 <λ3). There,
An objective optical element used in common for condensing the luminous flux emitted from each light source on the information recording surface of each information recording medium;
A first divergence angle changing element arranged between an optical path from the first to third light sources to the objective optical element and changing the divergence angle of the incident light beam;
It is disposed between the first to third light sources and the optical path from the first optical source to the objective optical element, and is movable between a first position on the optical path and a second position outside the optical path, and is disposed at the first position. A second divergence angle changing element that changes and emits the divergence angle of the incident light beam,
When reproducing and / or recording information on the first information recording medium, a light beam of infinite parallel light is incident on the objective optical element,
When reproducing and / or recording information on the third information recording medium, a finite divergent light beam is incident on the objective optical element,
2. An optical pickup device according to claim 1, wherein a position at which the second divergence angle changing element is arranged differs depending on whether the magnification of the light beam incident on the objective optical element is infinite parallel light or finite divergent light. The second divergence angle changing element is disposed at the first position when information is reproduced and / or recorded on the first information recording medium and the second information recording medium. Item 5. The optical pickup device according to Item 1. 3. The optical pickup device according to claim 2, wherein the second divergence angle changing element has a negative refractive power. The second divergence angle changing element is disposed at the second position when information is reproduced and / or recorded on the first information recording medium and the second information recording medium. Item 5. The optical pickup device according to Item 1. 5. The optical pickup device according to claim 4, wherein the second divergence angle changing element has a positive refractive power. 6. The optical pickup device according to claim 5, wherein the second divergence angle changing element is one of elements constituting a beam expander. The optical pickup device according to claim 5, wherein the second divergence angle changing element is a coupling lens. The optical pickup device according to claim 7, wherein the coupling lens is a collimating lens. 5. The recording layer of an information recording medium having a plurality of recording layers is switched by advancing and retracting an optical element having a negative refractive power among optical elements existing in the optical path. Optical pickup device. 2. The optical pickup device according to claim 1, wherein the first divergence angle changing element performs position switching in the optical axis direction. 11. The first divergence angle changing element performs position switching in the optical axis direction in response to the second divergence angle changing element moving between the first element and the second position. The optical pickup device described. The first divergence angle changing element when reproducing and / or recording information on the first information recording medium and when reproducing and / or recording information on the second information recording medium The optical pickup device according to claim 10 or 11, wherein the position is switched in the optical axis direction. A case where information is reproduced and / or recorded on the first information recording medium and a second information recording medium, and a case where information is reproduced and / or recorded on the third information recording medium, 12. The optical pickup device according to claim 10, wherein the position of the first divergence angle changing element is switched in the optical axis direction. It is disposed between the first to third light sources and the optical path from the first optical source to the objective optical element, is movable between a third position on the optical path and a fourth position outside the optical path, and is disposed at the third position. 14. The optical pickup device according to claim 1, further comprising a third divergence angle changing element that changes the divergence angle of the incident light beam and emits the light. 15. The optical pickup device according to claim 14, wherein the second divergence angle changing element and the third divergence angle changing element are exclusively located on the optical path. The second divergence angle changing element and the third divergence angle changing element may be positioned on the optical path at the same time, or may be separated from the optical path at the same time to constitute an optical system. 14. The optical pickup device according to 14. The optical pickup device according to claim 1, wherein the objective optical element is optimized for the first information recording medium. The optical pickup device according to claim 1, wherein the objective optical element is optimized for both the first information recording medium and the second information recording medium. The optical pickup device according to any one of claims 1 to 18, wherein the first light source to the third light source are light source units housed in a single package.

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